Which of the following compounds gives a ¹H NMR spectrum consisting of two singlets and a ¹³C NMR consisting of consisting of three signals?

Question

Quizplus · Accepted Answer

The NMR spectrum of a compound is based on the number of unique hydrogen environments present in the molecule.

Compound i has the following structure: 
H3C-CH=CH-CH2-Cl

There are only 4 hydrogen atoms in this compound and they are all attached to different carbon atoms. Therefore, four signals would be expected in the proton NMR, not two singlets and a triplet.

Compound ii has the following structure: 
CH3-CH2-CH(Br)-CH3

There are 8 hydrogen atoms in this compound and they should each give a unique signal in the NMR spectrum. Therefore, two singlets would be expected if all the hydrogens are chemically equivalent.

Compound iii has the following structure: 
CH3-CH2-CH(Cl)-CH2-CH3

There are 6 hydrogen atoms in this compound and they should each give a unique signal in the NMR spectrum. Therefore, three signals would be expected if all the hydrogens are chemically equivalent.

Compound iv has the following structure: 
Cl-CH2-CH(Br)-CH2-Cl

There are 8 hydrogen atoms in this compound and they should each give a unique signal in the NMR spectrum. However, there are two different types of hydrogens present: the two hydrogens attached to the bromine atom and the six hydrogens attached to the carbon atoms. Therefore, two signals would be expected for the hydrogens attached to the bromine atom and six signals would be expected for the hydrogens attached to the carbon atoms, totaling eight signals. This does not match the given NMR spectrum, so compound iv can be eliminated as a possible answer.

Therefore, the only compounds that match the given NMR spectra are ii and iii.

Which of the Following Compounds Gives a 1H NMR Spectrum

Which of the Following Compounds Gives a ¹H NMR Spectrum